1. Field of the Invention
The present invention relates to a power management method and device thereof, and more particularly, to a power management method and device thereof for improving power consumption.
2. Description of the Prior Art
Capacity and life time of a laptop battery has been greatly improved in the past few years. However, the power consumption of the processor increases and there are more and more computer equipments with high power consumption installed into new generation laptops, and thus that is the reason why power management becomes important. A good usage of smart power management can greatly improve life time of the battery without buying another battery.
Most hardware of the laptop can operate in different states according to different power supplies, such as stop, sleep, idle and working. In general, display, processor and hard disk consume most of the power on a main board. Though the basic input output system (BIOS) can directly perform power management without the operating system, it is more effective to achieve power arrangement via adding smart power management into the operating system to adjust power arrangement according to different situations, e.g. operating modes of drivers, the operating system and application programs, etc.
Therefore, the advanced configuration and power interface (ACPI) is developed for providing power state of the hardware managed by the operating system, so as to achieve power saving. The ACPI standard includes different power states S0-S5, which are defined as follows:
ACPIstatePower stateDescriptionS0WorkingThe system and the hardware are completely on.S1StandbyThe CPU is off, other hardware is on.S2PartialSome hardware is turned off.standbyS3StopOnly random access memory (RAM) and northbridge are on.S4HibernationThe system saves the contents of the RAM in thehard disk and the hardware is completely off.S5Soft offThe system appears to be off with very low power.
In other words, after the laptop entered the operating system, the ACPI standard and the BIOS supporting the ACPI can be utilized for performing power management. In addition, the ACPI can control the central processing unit (CPU) for power saving control to lower power consumption and operating temperature of the CPU. In general, the CPU supports power saving states C0-C3, from minimum to maximum power supply, respectively. The state C0 of the CPU indicates every portion and function of the CPU working with power supply, and the states C1-C3 indicate gradually turning off the power supply of each portion and function of the CPU. The CPU appears to be off in C3 state, only some clock signals or logic circuits provided from outer circuits have power supply. The power saving states of the CPU are not limited, for example, there is CPU supporting the power saving state C4 or thereafter, and the state number increases as the power saving level increases, but resuming time from power saving state to working state increases relatively.
However, there are still disadvantages within the operating system utilizing the ACPI for power management. For example, the operating system merely controls the hardware to enter different power states by the ACPI, e.g. the power saving state C0-C3 of the CPU, to achieve power saving, for extending life time of the laptop battery, but this power management lacks of flexibility. In short, the ACPI does not provide other mechanism to lower power consumptions of hardware, such as the CPU and display with great power consumptions, resulting in limitations of power saving performance. There is application software for providing relative mechanism to decrease power consumption of hardware, e.g. downgrade the operating frequency of the CPU when the laptop is turned from AC mode to DC mode, but this method causes serious degradation of the laptop performance.